In recent years, copying machines and printers utilizing electrophotography have made a remarkable progress in digitization and color printing. In the case of full-color images, a binder resin having a relatively low molecular weight is used to provide an enhanced color developability and a good fixability at low temperatures. However, if a such a low molecular binder resin is used and a heat roll fixing process is employed, an offset in which a toner is adhered to the heat roll can easily occur. In order to avoid this phenomenon, a process in which a fuser oil such as silicone oil is supplied onto a heat roll is employed.
However, the use of a fuser oil is disadvantageous in that the fuser oil is adhered to a recording medium such as a paper and a film for over head projector (OHP), to thereby stain hands and reduce the writability of copied matters by ball-point pen, pencil and felt-tipped marker.
In order to solve these disadvantages, JP-A-59-197048 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes a method which comprises incorporating a specific silicone oil in a toner mainly composed of a binder resin and a coloring agent to provide an enhanced offset resistance. Further, JP-A-63-271369 proposes a method for providing an enhanced offset resistance in which the softening point of the surface of the toner is raised than that of the core of the toner and a silicone oil is incorporated in the core.
However, these methods are disadvantageous in that the silicone oil and the binder resin have a poor compatibility with each other, thereby causing the silicone oil to migrate to the surface of the toner, toner blocking with time or chargeability change to deteriorate an image, etc.